This function applies V inverse via the Woodbury matrix identity
Vinv(G, qrM, tau_over_sigma, sigma, RHS)Matrix of genotype markers (size n x L)
Pre-computation for LxL linear system solve
Tau over sigma from precomputation
Variance component from model noise epsilon
Matrix or vector on right-hand side of V inverse
Matrix or vector resulting from left multiplication of Vinv with input RHS